President Trump’s campaign has filed an arbitration action against Omarosa Manigault Newman, alleging that the former White House aide, who just published a tell-all book, has broken a 2016 confidentiality agreement, a campaign official said Tuesday.

The action, which the campaign said was filed in New York, comes amid a publicity tour by Manigault Newman to promote her book, “Unhinged,” which portrays Trump as bigoted and racist and questions his mental capacity.

During a television appearance Tuesday afternoon, Manigault Newman said she didn’t believe she had violated the agreement.

“It’s interesting that he’s trying to silence me, so what is he trying to hide? What is he afraid of?” she said on MSNBC. “I think he should be afraid of being exposed as the misogynist, the bigot and the racist that he is.”

The Washington Post has not seen a nondisclosure agreement signed by Manigault Newman during the campaign, but copies of other agreements signed by aides include broad prohibitions on behavior and appear to be drawn heavily from similar contracts used by the Trump Organization, the president’s family firm.

Under one such agreement, signers promised not to “demean or disparage publicly” Trump, his company or any member of his family. Signers also agree to participate in binding arbitration at Trump’s discretion if a dispute arises over the agreement. Trump also reserves the right to take signers to court.

Trump has threatened legal action against book authors and other perceived adversaries but has not followed through on many occasions.

It was not immediately clear what Trump’s campaign, which was headquartered in New York in 2016, was hoping to achieve with its action filed with the American Arbitration Association.

The action comes as Trump has publicly disparaged Manigault Newman, the former reality television star who was the highest-ranking black employee in the White House.

Writing on Twitter on Tuesday morning, the president called her “that dog” and a “crying lowlife,” and he praised his chief of staff, John F. Kelly, for firing her last year.

At a regular briefing Tuesday, White House press secretary Sarah Huckabee Sanders declined to say whether she or any other specific staffers had signed an NDA, although she described the practice as commonplace.

“I’m not going to get into the back and forth on who has signed an NDA here at the White House,” Sanders said. “I can tell you that it’s common in a lot of places for employees to sign NDAs, including in government, particularly anyone with a security clearance.”

Yet NDAs have not been widely used by past administrations outside the transition time between presidents, in part because most legal experts believe such agreements are not legally enforceable for public employees.

David Axelrod, President Barack Obama’s former counselor, said it would be “unthinkable” for aides to sign such agreements.

In her book, Manigault Newman writes that the Trump campaign offered her a $15,000-a-month job upon leaving the White House in exchange for signing a broadly worded NDA that would have barred her from disclosing details of her tenure in the administration. That agreement was never signed, she said.

Trump said on Twitter on Monday that Manigault Newman had signed an earlier agreement.